Coating composition



quality improvement and ing compositions 1 been possible. A

Patented 'July as. 1942 COATING COMPOSITION Johan. a. I. (in

mington,

No Drawing.

Lowell, South River, N. 1.,

Pont de Nemours a; Company, Del, a corporation of Delaware ApplicationNovember 28, 1939,

assignor to Wil- Serial N0. 306,49!

4 Clam. (Cl- 106-191) This invention relates to improved nitrocelluloselacquer compositlons and more particularly to lacquer compositionssuitable for spray application.

The prior art shows clearly" a continuing struggle for higher solids atspraying viscosities. Many of the suggestions made failed completely. Alimited number has been adopted commercially and has been hailed asbeing revolutionary in their effects. 01 these, Reissue Patent 16,803,

disclosing the use of low viscosity nitrocellulose,

' is the most important in that a great majority of the cellulosenitrate compositions sold today are based upon it. Continued developmentwork on new modifying agents, particularly on synthetic resins,gradually permitted the art to use cellulose nitrate of lower and lowerviscosity characteristics. New compatible polyhydric alcohol-polybasicacid resins were discovered and these in many instances could be used inlarger amounts. Literally hundreds of non-volatile liquid organicplasticizers were developed and tested in attempts to further increasethe solids at spraying ty. In short, many means of increasing the solidsand lowering the cost of the lacquer compositions has been resorted to.

The present invention is concerned with reducdiflerential describedabove to coating compositions through important improvements in thecompositions, without. detracting from the inherently superior qualitywhich characterizes this-type of composition.

This invention has as its primary object the provision of coatincompositions whereby substantial economy in material and operating costsis secured. Another object is the provision of coating compositionshaving higher solids at room temperature spraying viscosity than hasheretofore been possflile. Another object is the sprayed at normalspraying'viscosity give coating thicknesses considerably beyond normalexpectations. A further object is the provision of coatwhich can besatisfactorily sprayed at viscositiw greater than has thus far stillfurther object is the procompositions which can be sprayed readilywithout sacrifice in desirable qualities demanded by the user, mumdurability and toughness.

These objects are accomplished through the use in cellulose nitratelacquers and enamels. of extremely powerful, balanced solventcombinations for cellulose nitrate as hereinafter disclosed.

By solvent combinations, I mean all the volatile ingredients present inthe lacquer at the instant of spraying, including the active solventsfor cellulose ents such as alcohols and the aliphatic and aronitrate,and also non-solvent diluethyl ketone,

' provision of coating compositions which when suchas maxithem withlacquers of matic hydrocarbons (e. g., toluol and gasoline). Some ofthese active solvents are acetone, methyl methyl propyl ketone; methylisobutyl ketone, methyl acetate, ethyl acetate, the normal, isoandsecondary butyl acetates, the isomeric amyl acetates, cyclohexylacetate, ethyl propionate, ethyl butyrate, ethyl caproate, methylformamide, ethyl ether of ethylene glycol, ethyl ether ofdiethyleneglycol, the acetate of ethyl ether of ethylene glycol,propylene oxide, isobutylene oxide and many others. Certain combinationsof non-solvents show solvent power as, for example, ethyl ether-ethylalcohol. These solvents differ markedly in volatility as well as intheir solvent power for nitrocellulose.

Solvent power has been measured by a number of methods, each of whichties in with the usage to which the measurement is to be put. In thisdisclosure I prefer to evaluate solvent power as the viscosity of asolution of a definite quantity of dry. nitrocellulose by weight in anequally definite quantity of solvent or solvent combination whenmeasured at a temperature of 25 C. in any form of a calibratedviscosimeter, whereby it is possible to express the values in standardviscosity units (centipoises).

The amount of cellulose nitrate present in a spray lacquer is limited bythe maximum viscosity at which out difficulty by spraying. The optimumviscosity ranges of the present art for satisfactory spraying have beenfound to be in a very narrow range, dependent upon the type of sprayequipment used. The optimum viscosity range for the spraying of clearfurniture lacquers has been found to be 50 I to 85 centipoises, whilefor pigmented automotive enamels the viscosity range is 20 to 50centipoises. These ranges are limitative only in that the best practicalresults are obtained by using the present art.

I have discovered that improved high solids cellulose nitrate sprayinglacquers result when I greatly reduce or even practically eliminate frommy solvent combination low boiling, non-solvent diluents such as benzol,toluol and the gasoline type substitutes for benzol and toluol, as wellas excessive portions of ethyl alcohol, and for these substitute highlyactive low boiling solvents such as acetone, methyl ethyl ketone, methylacetate or ethyl acetate, without necessarily altering the proportionsand balance of the less volatile active solvents, alcohols and diluenthydrocarbons normally present in commercial spraying lacquers.

I further limit myself to total solvent combinations having a solventpower for lacquer type nitrocellulose, as measured by viscosity, of notless than about that of absolute ethyl acetate for the same sample ofnitrocellulose, that the lacquer can be applied withiently determineWhether any solvent or solvent combination fulfills this requirement, asolution.of a nitrocellulose of about 12.0% nitrogen content and aviscosity characteristic of about Hercules should be prepared and theviscosity measured by any conventional means. Table '2 includes resultsof this test applied to several commercial solvents.

I have found that the new compositions possess the unexpected quality ofease of spraying at viscosities above those now considered optimum forcommercial work. I have also discovered that the compositions havebetter flowing or smoothing-out characteristics at the end of thespraying operation. The lacquers also function in an unexpected fashionin giving increased coating thicknesses all out of proportion to theincrease in lacquer solids at the spray gun.

. My discovery accomplishes seven chief benefitstem erature reductionoccurs during the spraying which causes too great a condensation ofmoisture from the air on the sprayed lacquer coat and this moisture willbecome entrapped in the drying film unless solvents less volatile thanwater are present. It is, therefore, to be understood that by a balancedsolvent combination I mean either a single solvent or a combination of.solvents which can be sprayed without ex-- cessive loss and which alsohave the power of eliminating precipitated moisture before the sprayedfilm sets up to a gel state.

The term high solids as used herein refers to my findings that whenusing the improved type of solvent compositions described, I obtain ahigher concentration of solids at spraying viscosity than has beenobtained with previous solvent compositions considered satisfactory forspraying.

It is well known that commercial compositions must deposit films thatare as free as possible from excessive spray dust and blushing. The newcompositions are entirely satisfactory in these respects.

It is a known fact that under a given set of conditions, each volatileingredient has a specific temperature depression effect when sprayed andalso that a definite percentage will be dissipated into the air. Thecombined depressions and losses measure to a great extent-the behaviorof a solvent combination during spraying.

In order to illustrate this point, an experiment has been carried outwith a DeVilbiss spray gun (type CH, tip #92), during which a variety ofsolvents has been sp ayed individually and the temperature depressidetermined. The air pressure at thehgun when spraying was 50 (1) Lowerviscosity at any definite solids than pounds, and the air temperature ata distance of 10 inches from the tip of'the gun was 23 C.

' At this point the relative humidity of the air was 18%.

Table 1 Vapor pres- Temperasolvent used sures ture depres- 25 C sion Mm.c

Ethyl alcohol (95% by volume) 57. 5 l9. 0 Isobutyl alcohol 14. 0 8. 9n-Bntyl alcohol- 1 7. 3 6. 5 Isoamyl alcohol 5.6 Ethyl acetate (99%)..90.0 25. 5 Isobutyl acetate 17.0 12.3 n-Butyl acetate (90%) 13. 5 9. 2Isoarnyl acetate (85%).. 6. 3 Acetone 220. 0 35. 0 Methyl ethyl ketone-93. 0 24. 0 Methyl n-butyl keton 14. 0 9. 7 Toluol 29. 0 l4. 9 Xylol 6.7 7. 2 High solvency petroleum naphtha (l35 O.) 15.0 High solvencypetroleum naphtha (MO- C.) 5. 2 Water 23. 5 11.2

'The term low boiling solvents or diluents is a phraseology generallyaccepted by the art. However, its meaning has not been suflicientlyspecific to define its limits. Therefore, low boiling" as it is used inthis disclosure refers to organic liquids which on spraying show atemperature depression characteristic equal to or greater than toluol.Expressed in terms of the data collected, this means that any'volatileorganic liquid having a temperature depression of at least about 15 0.,when water sprayed under the same conditions shows a temperaturedepression of 11.2 C. and toluol of 14.9" C. is a low boiling material.

In my process I control the proportions of volatile ingredients in sucha manner that the evaporation losses during spraying produce results notfound in prior art volatile components. that some loss insolvent poweroccurs during spraying, coupled with the reduction in the ratio ofsolvent to solids as the material hits the surface, means that theviscosity is very much great- -er than at the spray gun. Added to thisis the the viscosity'has increased several-fold in the extremely shortpassage of the lacquer from the gun to the object being coated. I havefound that it is this increase in viscosity which allows the applicationof abnormally thick coatings with solvent compositions in thisdisclosure.

It is common practice at present to use as great a proportion of highlyvolatile ingredients as possible and still obtain satisfactorysmoothing-v out of the coatings. I have found that the use of highlyvolatile non-solvent diluents in considerable amounts, as has been thepractice, sharply limits the quantity of more powerful solvents that canbe used, and also that such a practice limits the solids content in thelacquers as sprayed. I have discovered that by reducing the low boilingThe fact diluents such as toluene, gasoline, and ethyl alcohol verygreatly and directly substituting for them low boiling active solventssuch as ethyl acetate or methyl ethyl ketoneas well as smaller amountsof acetone, I obtain solvent combinations new to the spray art.

The viscosity of nitrocellulose in absolute ethyl acetate is much lowerthan the viscosities secured with the great majority of activenitrocellulose solvents. So, in order to secure solvent combinationswhich will have a solvent power at least 80% that of absolute ethylacetate, I blend active cellulose nitrate solvents of high volatilityand high solvent power with active solvents of low volatility andattendant lower solvent power along with non-solvent diluents to give anaverage solvent power in my specified range and with sprayingcharacteristics more than comparable with the present art.

It is well known that substantial viscosity reduction can be producedthrough the use of small quantities of the lower aliphatic alcohols suchas ethyl, propyl, butyl and amyl alcohol in combination with the activesolvents. I prefer to make the best possible use of small amounts ofthese alcohols to give the minimum viscosity characteristics but alwaysonly after practical spraying tests show that the other desirablequalities are not lost thereby. 4

Benzol, toluol, xylol and gasoline are the hydrocarbon diluents mostcommonly disclosed in the prior art. Benzol is objectionable because oftoxicity and toluol now ranks as the most important aromatic hydrocarbonused. I can and do make use of relatively smaller amounts of toluol whenit is necessary to secure a perfect compatibility relationship betweenthe nitrocellulose and the resin modifiers, either natural or synthetic.Aliphatic hydrocarbons of the gasoline type either before or aftercracking or hydrogenation, are now widely used by the art principallydue to the low cost. I prefer to use the special lacquer type gasolinethinners which contain appreciable percentages of unsaturated branchedchain hydrocarbons as they are more nearly equivalent to the efficiencyof toluol than are the straight chain gasolines.

Certain resins such as damar show incompatibility in the presence ofhigh alcohol concentrations and one skilled in the art will avoidnoncommercial compositions by a proper balancing of the diluents andalcohols. Thus, it will be seen that certain modifying ingredientsprevent the use of hydrocarbon-free lacquers.

In general, I prefer to employ solvent combinations containing lowconcentrations of non-solv-ent hydrocarbon diluents having evaporationrates greater than that of water and in most cases the proportion ofthis type of material should not exceed 15% by weight of the totalsolvent combination. I also prefer to include active cellulose nitratesolvents in predominant proportions, in general, not less than about 1times the amount of non-solvent diluents.

It has been explained that in general high solvent power and highvolatility go together. This is particularly true in any homologousseries of organic solvents. As a class the ketones are better solventsthan the esters at the same range of volatility, and of the esters theacetates are more powerful solvents than the esters of the higher fattyacids such as propionic and butyric. The following table is given inorder to illustrate the difference in the solvent power expressed inviscosity units of several of the solvents described,

and also to show the fact that as the volatility in any class ofcompounds decreases, the solvent power also decreases very considerably.The data also show a surprisingly small number of solvents which alonecan be considered to have a solvent power at least that of ethylacetate.

Table 2 Viscosity (centipoises) Acetone 50 Methyl ethyl ketone Methylpropyl ketone 109 Methyl acetate 145 Ethyl acetate 152 Methyl n-butylketone 215 n-Butyl acetate 255 Isobutyl acetate 2'70 Isoamyl acetate 400Methyl ester of ethylene glycol 460 Ethyl ether of ethylene glycol; 495

A clear furniture lacquer was prepared having the following composition:

High solvency petroleum naphtha 140-190 This lacquer was compared with astandard commercial furniture lacquer of known utility having thefollowing composition in which the ratio of the solids ingredients isidentical with the high solvency formula but with 26.2% solids contentas compared with 32.9% for the high solvency type:

EXAMPLE 2 Per cent by weight Nitrocellulose A; sec. viscosity) 10.9 Rawcastor oil 1.6 Dibutyl phthalate 2.9 Maleic acid modified rosin ester10.9 Denatured ethyl alcohol 8.5 Absolute ethyl acetate 6.0 n-Butylacetate 22.0 n-Butyl alcohol 3.5 Toluol 33.7

The viscosity of the high solvency lacquer of Example 1 at optimum sprayperformance was found to be centipoises as compared with 60 centipoisesfor the standard furniture lacquer of Example 2 after tests had beenmade to show that the high solvency formula could be sprayed at thehigher viscosity with better results. Additional viscosity tests showthat in the case of the high solvency type, a solids concentration of29% was secured at a viscosity of 60 centipoises. Thus, we show that atthe same viscosity, at the gun, the use of the more powerful solventcombination allowed an increase of 11% in solids, but that taining 24%increase in solids over that of thestandard prior art furniture lacquer.A spraying test on Example 1 was carried out in a'room at 25 C. and at arelative humidity below 30%. Example 1 was sprayed at a viscosity of 100centipoises at 25 C. through adistance of inches and collected forexamination. The solids were found to be 40.0% as compared with 32.5% atthe start. The temperature had dropped to 14 C. or a drop of 11 C. andthe water content had jumped from 0.84% to 1.50%. The viscosity of thecollected material at 14 C. was very close to 1000 centipoises.

The sagging tendencies of thick wet coats of lacquer on a verticalsurface are highly dependent upon the viscosity of the lacquer as ithits the object. The higher the viscosity of the lacquer, the thickerthe allowable coating. The securing of the major portion of solventpower through the use of high concentrations of very volatile activesolvents permits me to obtain an abnormal rise in viscosity because ofthe markedly greater loss in solvent power during spraying brought aboutthrough high losses of these highly volatile active solvents.

The spray tests gave unexpected results in resultant thickness of filmwhen the new compositions were applied to a wood surface. It was foundthat the standard prior art furniture lacquer (Example 2) could besprayed onto-a vertical surface at a dry film thickness of 1.2 mils in asingle coat. Any substantially thicker film gave sagging or running ofthe lacquer film during the drying of the panel. The high solvencylacquer (Example 1) when sprayed onto a vertical surface in one coatgave a, dry film thickness of 2.2 mils, and in some instances it waspossible to obtain a film thickness of 2.5 mils before air bubblesappeared in the film. It was also determined that a dry film thicknessof 2.8 mils could be obtained from the high solvency lacquer beforedefinite sagging tendencies became noticeable. Thus, with an increase of24% of solids at the gun, the new solvent formula permits theapplication of a film at least 83% thicker than that secured with theprior art film. This great increase in film thickness was entirelyunexpected and gave rise to greatly stimulated research in the study ofspraying compositions. .An explanation as has been discussed above isthat due to the high percentage of the highly volatile methyl ethylketone in the high solvency formula, which solvent tends to disappearrapidly during spraying, a much greater increase in viscosity occursduring the spraying operation, so that the wet coat of lacquer on thewood has a much higher viscosity than is the case with the prior artmaterial. I

Utilization of the temperature depression data given in Table 1 can bemade in a further analysis of the difierences between the solventcombinations of Example land Example 2. It has been found that the totaltemperature depression of a combination of solvents can be closelyapproximated by multiplying the temperature depression characteristic ofthe individual solvent by the weight percentage of that material presentin the combination. The sum of these individual depressions is, withvery few exceptions, substantially equal to the temperature depressionobtained through the actual spraying of the combination. Therefore, theanalysis of new solvent combinations is made possible provided that arepresentative set of data on the temperature depressions of any groupof volatile organic liquids has been obtained. As has been pointed out,the conditions prevailing during the spraying of solvents make majordifferences in the actual numerical temperatureadepression dataobtained, but when all materials under test are evaluated undercarefully controlled conditions, the results secured are extremelyuseful and directly comparable. In the analysis of this particularproblem, the data given in table 1 will be considered to be fullyrepresentative of the temperature depressions obtained under one set ofspraying conditions.

Thus, the volatile ingredients in Example 1 give a calculated totaltemperature depression of 14.8 C., of which total temperature depressionthe methyl ethyl ketone contributes 62% while the hydrocarbon diluentscontribute only 5.6%. Compare this with Example 2 where the temperaturedepression is found to be 13.6 C. and where the low boiling activesolvent represented in this case by ethyl acetate contributes only 15%of the total temperature depression, whereas 47% is caused by thehydrocarbon diluents present. One of the most important points of thisanalysis is that the total temperature depressions of useful sprayingmixtures lie in a very narrow range which, when utilizing the data inTable 1, can be expressed as 13.5-15.5 C. Thus, we can show that eventhough we are utilizing, in the case of Example 1, a solvent mixturecontaining 38.6%

methyl ethyl ketone by weight, this abnormally high concentration of lowboiling active solvent does not cause excessive temperature depressionand its resultant high blushing tendencies. Also, if the temperaturedepression is more than 16 C.,- excessive precipitation of water fromthe atmosphere will occur during spraying under humid conditions leadingto the typical and. widely prevalent phenomenon of blushing. On theother hand, if the temperature depression is less than 13 C., themixture will be markedly slower drying and the sprayed coating will, ingeneral, have an excessive sagging tendency when applied in thick coatsto a vertical surface.

In many cases it has been found advantageous to use considerable amountsof high boiling hydrocarbon diluent as the presence of these in thesprayed, wet film tends to greatly increase the viscosity and overcomessagging to a marked degree. It is important, however, that less thanabout 25% of the total temperature depression is due to the presence ofhydrocarbon diluents.

EXAMPLE 3.--Blaclc enamel *invention permits spraying at a substantiallyhigher viscosity than the present art.

This enamel which incorporates the principles of my invention wascompared with a standard black automotive enamel having the identicalsolids ratio, but at a solids content of 13.9% as compared with 20.7%possible with the improved solvent combination.

Damar res 1.7 Synthetic resin 1.7 Dibutyl phthalate 1.6 Blown castoroil". 0.9 Carbon black 1.1 Denatured ethyl alcohol 8.7 Isopropyl acetone2.2 Methyl ethyl ketone 7.3 Isobutyl acetate 17 .5 Isoamyl acetate 6.8Isobutyl alcohol v 3.1 Isoamyl alcohol 2.7 High solvency petroleumnaphtha (140- 190 C.) High solvency petroleum naphtha (95- The syntheticresin used in these compositions consisted of a reaction product of thereaction having been carried out according to methods already well knownto the art.

The enamels are prepared in steps, the first of which represents thedispersion of the carbon black in a heavy duty kneading machine in acolloid consisting of a portion of the nitrocellulose, dibutyl phthalateand solvents whereby a very stifi paste is formed and continuing thekneading action until the dispersion had reached a predetermined point.Dispersion can be secured by other procedures such as rolls grinding orpebble mill grinding provided suitable proportions of the availableingredients are used to give the optimum dispersion eflfects.

The remaining nitrocellulose is then converted into a solution by usinga portion of the remaining solvent combination. The pigmentedintermediate, nitrocellulose base, resins, plasticizers and solvents arethen mixed together by means of an eflicient paddle type mixer untilhomogeneous.

In commercial practice, it is customary to prepare a concentrated enamelfor shipment to the user and to provide a thinner free from solidmaterial to allow the user to thin as desired. For the purposes of thisdisclosure and to simplify the disclosure,- the composition of the .riedout on large sheets of tenders and on auto bodies on a commercial pro-Comprehensive spraying tests were then carautomotive steel, on

duction line. In all cases it wasround possible to obtain in three'coats a lacquer thickness with sion of Example 4 is 14.36

thinned material is being used to illustrate the products of theinvention, it having been my experience that unless this is done, it isimpossible for any except those skilled in the art to understand theprinciples involved.

The viscosity of the improved enamel of Example 3 at the point ofoptimum spraying characteristics was 43 centipoises ascompared with theconventional enamel of Example 4 at 20 centipoises, showing again as inExample 1 that my the improved formula equivalent to six coats with theconventional formula.

Thus, with an increase in total solids of only 50%, and this increaseinsolids possible only through the improved spraying characteristics, ithas been found that an increase of in film thickness per coat is readilysecured 'without loss in quality of the'applied coat. In fact,.

improvements in flowing but, greater resistance to atmosphericconditions and less rubbing and polishing occurred when using theimproved composition.- The-results were substantially all out ofproportion to those predictable in the light of past experience.

Analyzing Examples 3 and 4 by means of the temperature depression datagiven in Table 1, we find that the total temperature depression of thevolatile ingredients in Example 3 is 14.9 C., of which methyl ethylketone contributes almost exactly 51% and the hydrocarbon diluentscontribute only 7%; The total temperature depres- C., of which the lowboiling active solvents, specifically acetone and methyl ethylketone,contribute only 20% of the total temperature depression, whereas thehydrocarbon diluents contribute 41%, or a major portion. Here again, asin Examples 1 and 2, we are able to 'show by a simple calculation, howit is the particular advantages of higher solids at 1 sprayingviscosity, higher actual spraying viscosity,'and abnormally thickerspray coats, could be obtained commercially if abnormal increases intemperature depression were brought about by these formulations.Therefore, I do not substantially depart from the temperature depressionrange of from 13.5 to C.

These examples show instances in which'from 51% to 62% of the totaltemperature depression is due to thepresence of low boiling activenitrocellulose solvents having a temperature depression greater than 15C. However, I am not limited to these high values and'have obtainedimproved, useful compositions within the range of 40 to 80% of totaltemperature depression due to the presence of these low boiling, highlyvolatile and highly active solvents, although I prefer compositions inwhich from 45 to 65% of the total temperature depression is caused bythese active solvents.

Many other compositions falling within the scope of my disclosure havesince been studied, and in every instance it has been found possible tomake important savings in the costs of application, and in all cases ithas been possible to apply thicker coats.v

Substantially my invention as disclosed results in the production ofnitrocellulose lacquers and enamels having .a higher solids content atspraying viscosity than prior art enamels. In addition, a furtherincrease in solids at the spray gun has been secured because of thehigher viscosity at which the lacquers can be sprayed. Whensprayed thesolvents in the enamels show. less of a temperature depression per unitof solids applied, thus lessening the amount of moisture precipitatedfrom the air during the spraying able for spraying, and in thisinvention derivatives of cellulose such as cellulose acetate, or otheresters, or ethers of cellulose are not equivalents.

I can make use of almost every ingredient developed for and found usefulin the lacquer art;

thereby permitting the formulation of products of maximum durability andutility at a substantially lower consumption of. volatile solvents andmore particularly products costing less to apply,

thus effecting major economies for the user.

Also, I may prepare these products in any conventional manner, makinguse of standard equipment and manufacturing procedures.

Inasmuch as the process of spraying is substantially different frombrushing, dipping, roller coating, knife coating, casting and flowcoating, the efliciency of my invention is specific almost entirely tothe spray art. In general, while it is possible to 'use this disclosureto prepare materials readily applied by these other procedures,

' the abnormal difierences in coating thickness will not be found beyondthe fact that the preferred solvent combination will give high solidsconcentrations at any specified viscosity.

It is apparent that many widely different embodiments of the inventionmay be made without departing from the spirit and scope thereof; and,therefore, it is not intended to be limited except as indicated in theappended claims.

I claim: Y

1. A spraya'ble, blush-resistant, high solids coating compositioncomprising cellulose nitrate and a volatile liquid organic vehicle whichhas a solvent power for cellulose nitrate of at least about 80% that ofabsolute ethyl acetate as measured by the viscosity of equal percentagesoluabout 80% that of absolute ethyl acetate as measured by theviscosity of equal percentage solutions, and which has a calculatedtemperature depression characteristic during spraying of between 13.5and 155 0. when water sprayed under the same conditions gives adepression of about 112 0., of which temperature depression 45 to 65% iscontributed by the partial evaporation of cellulose nitrate solventshaving a temperature depression greater than that of toluol.

3. A sprayable, blush-resistant, high solids coating compositioncomprising cellulose nitrate and a volatile liquid organic vehicle whichhas a solvent power for cellulose nitrate of at least about 80% that ofabsolute ethyl acetate as measured by the viscosity of equal percentagesolutions and which has a calculated temperature depressioncharacteristic during spraying of between 13.5 and 15.5 C. when watersprayed under the same conditions gives a depression of about 11.2 C.,of which temperature depression 40 to 80% is contributed by the partialevaporation of cellulose nitrate solvents having a temperaturedepression greater thanthat of toluol and less than 25% is contributedby hydrocarbon diluents. a

4. A sprayable, blush-resistant, high. solids coating compositioncomprising cellulose nitrate and a volatile liquid organic vehicle whichhas a solvent power for cellulose nitrate of at least about that ofabsolute ethyl acetate as measured by the viscosity of equal percentagesolutions, and which has a calculated temperature depressioncharacteristic during spraying of between 13.5 and C. when water sprayedunder the same conditions gives a depression of about 112 C., of whichtemperature depression 45 to 65% is contributed by the partialevaporation of cellulose nitrate solvents having a temperaturedepression greater than that of toluol and less than 25% is contributedby hydrocarbon diluents.

JOHN H. LOWELL.

